The present disclosure relates generally to automobile steering systems and, more particularly, to a method for automatically adjusting reference models used by vehicle stability enhancement systems in response to a change in steering mode.
Certain Vehicle Stability Enhancement (VSE) systems currently in existence typically employ a xe2x80x9cReference Modelxe2x80x9d algorithm that calculates a desirable handling motion for the vehicle. Such reference model algorithms have historically assumed that the desirable handling motion of the vehicle is solely a function of handwheel angle and vehicle speed. However, with the advent of new vehicle systems such as four-wheel steering, rear wheel steering, front controlled steering, active roll control and the like, the desirable handling motion may change when the new system state changes (e.g., as a result of driver preference changes or initial system activation). Thus, the existing reference models are typically not sufficient for use in a VSE system with multiple modes of steering, wherein each steering mode may have different desirable handling responses associated therewith. xe2x80x9cDriver""s preferencexe2x80x9d is a feature available in certain electric front controlled, rear controlled or fourwheel automobile steering systems. A driver""s preference switch may include settings such as xe2x80x9csportyxe2x80x9d, xe2x80x9cnormalxe2x80x9d, xe2x80x9ctraileringxe2x80x9d, xe2x80x9csystem offxe2x80x9d, or other modes representing various vehicle-handling objectives.
In early development of procedures to provide vehicle dynamic stability certain Vehicle Stability Enhancement (VSE) systems, employ separate look-up tables for the xe2x80x9cReference Modelxe2x80x9d algorithm that calculates a desirable handling motion (e.g., desired yaw rate) for the vehicle when operating in two wheel, normal four wheel or special trailer mode control for the rear wheels. When a change in the open-loop rear steer angle command was made to provide a different driver xe2x80x9cfeelxe2x80x9d based upon customer preferences, the look-up table had to be re-tuned to the new performance characteristic.
This design approach increased the size of computer memory used for tabular data storage and computational selection of each variation possible. Moreover, under this older design approach the development cycle was slowed because new calibrations for the look-up table were required whenever changes were made to the Vehicle Stability Enhancement (VSE) systems.
The above discussed and other drawbacks and deficiencies of the prior art are overcome or alleviated by a method for automatically adjusting a vehicle stability enhancement (VSE) system, the VSE system used in conjunction with a steering system having a plurality of driver-selectable steering modes associated therewith. In an exemplary embodiment, the method includes configuring a reference model within the VSE system to generate desired vehicle handling aspects, the desired vehicle handling aspects being a function of one or more driver inputs to the steering system. Then, a determination is made as to which of the plurality of driver-selectable steering modes is activated, wherein each of the desired vehicle handling aspects generated is made further dependent upon a specific steering mode selected and wherein the desired vehicle handling aspects comprise a desired steady state yaw rate; and the driver inputs include an effective road wheel position.
In a preferred embodiment, desired vehicle handling aspects include a desired steady state yaw rate. The one or more driver inputs further include a handwheel angle (HWA) and a vehicle speed. In one embodiment, the method further includes configuring a lookup table for generating each of the desired vehicle handling aspects, wherein each lookup table is configured to include entries corresponding to a selected steering mode. The lookup table corresponding to the desired steady state yaw rate has the effective road wheel position as a first input thereto, and the vehicle speed as a second input thereto.